1. Field of the Invention
The present invention relates to an apparatus for assembling a car body on an assembly line and, more particularly, to an apparatus capable of assembling main bodies of cars of various kinds or types.
2. Description of the Prior Art
To assemble the main body of a car, the prior art resorts generally either to equipment of a special machine type or to equipment of a circulating jig type. In the special machine type, a plurality of assembly stages are each equipped with special jigs for each kind or type of car, to receive and assemble body parts. Equipment of the circulating jig type is equipped with jig trucks specifically for each kind or type of car, the jig trucks being circulated while being loaded with the body parts, so that the necessary jig trucks may be brought into a single assembly station to assemble the proper body parts for each car body.
More specifically, the special machine type of equipment is provided at one assembly station, as shown in FIG. 8, with a first jig 51 for under bodies and a pair of second jigs 52 (one one shown) for side bodies. The first jig 51 is loaded with an under body A by successive upward-forward-downward-backward movements of a transfer machine which is equipped with a transfer bar 53; whereas each of the second jigs 52 is loaded with a side body B from an overhead conveyor (not shown) by tilting an openable frame 54 supporting said second jig 52. Upon completion of the positioning operations of the aforementioned first and second jigs 51 and 52, the under body A and the side bodies B are then assembled by welding means (not shown) which is composed primarily of a welding gun provided especially for this purpose.
After completion of these assemblies, the partly assembled body is shifted to a next station where a car roof C is fed downward from a roof conveyor 55 and is assembled to the side bodies. After this, sub-body parts such as a cowl, an upper back, and a lower back are fed at different stations from special conveyors similar to the roof conveyor 55 and are added to the assembly until the main body is completed.
On the contrary, the jig circulating type of equipment is provided, as shown in FIG. 9, with a first jig truck 56 for the under body and a pair of second jig trucks 57 (only one shown) for the side bodies such that they circulate in separate loops independently of each other. The first jig truck 56 moves on a floor 58, while carrying an under body A to an assembly station; whereas the second jig trucks 57 move is suspended states, while carrying the side bodies B to the assembly station. At this assembly station, as shown, the first jig truck 56 and the second jig truck 57 are connected so that the under body A and the side bodies B then can be assembled by welding means. After this assembly, the roof C and the sub-body parts are assembled in the same way as with the aforementioned special machine type of equipment in accordance with predetermined steps until the main body is completed.
In the special machine type of equipment, the kinds of cars handled by one set of jigs are restricted more or less to a single body type (such as sedan, van, or coupe body models) and can be interchanged only by replacing the jigs 51 and 52. The special machine type of equipment presents a problem, therefore, in that it is poorly adapted to handle more than one car body model or to accommodate design changes for producing a new model car.
On the other hand, the jig circulating type of equipment is able to accommodate a plurality of car kinds and types merely by changing the loading orders for the jig trucks 56 and 57. Because the parts are positioned for assembly only by connecting the jig trucks 56 and 57, however, the jig circulating type equipment has the problem that the positioning accuracy is likely to have a large tolerance. Also, a number of jig trucks have to be prepared for the circulating conveyor.
A further problem shared by both of the aforementioned two types of equipment, is that the large number of assembly stations increases the cost and space for facilities and makes it impossible to achieve the desired productivity increase.